. PROJECT SUMMARY (See instructions): This program project uses an innovative approach to investigate the association of total and compartment specific body fatness with cancer risk in a multiethnic population. The protocol involves re-contacting 2,000 participants in the Multiethnic Cohort (MEC) Study (200 each in 10 sex-ethnic groups) for direct characterization of body fat amount and distribution using whole-body DXA and abdominal MRI and to obtain biospecimens and questionnaire data. Models that incorporate lifestyle behaviors and markers of blood biochemistry, genomics, metabolomics and the gut microbiome will be built to best predict each of several adiposity phenotypes (total fat mass, trunk-to-periphery fat ratio, visceral fat, deep and superficial abdominal subcutaneous fat, liver fat). Next, these predictors, taken as surrogates for the adiposity phenotypes, will be tested in nested case-control studies for association with breast (n=1,217 cases) and colorectal cancers (n=1,379 cases) using pre-diagnostic biospecimens and questionnaire data that are already available in the MEC. The role of the Recruitment & Data Collection Core (Core B) is: 1) to recruit the 2,000 MEC participants for the cross-sectional study of adiposity phenotypes and to perform the data and blood/stool specimen collection; 2) to collect a stool sample by mail from an additional ~4,200 MEC subjects for whom GWAS genotype data are already available; and 3) to retrieve and ship the newly collected and previously stored biospecimens for the laboratory analyses by the four research projects in the P01. Recruitment for the cross-sectional study will occur during the first 3.5 years and involve close coordination between the two MEC study locations, with the assistance of the Body Fat Compartments Imaging Core (Core C) and the Data Management & Analysis Core (Core D). The University of Hawaii Cancer Center will re-contact 1,200 Japanese American, Native Hawaiian and white cohort members aged 65-70 years residing on Oahu, Hawaii. The University of Southern California will re-contact 800 African American and Latino participants residing in Los Angeles. Both sites have access to a clinical research facility for data collection and imaging, and are highly experienced in conducting studies with similar protocols on the MEC population.